Adjustment amount for shipping price is a negative value.
This error occurs when the Shipping value in an adjustments feed (XML) is a negative value. If you uploaded a tab-delimited adjustments file, this error occurs when the shipping-price-adj value is a negative value. Shipping and shipping-price-adj must be a positive value representing the refund amount you wish applied to the Shipping or shipping-price component of an order.
You cannot charge a customer's credit card by supplying a negative value.
To resolve this error resubmit your adjustment data with a positive Shipping or shipping-price-adj value.